1909. } The Wave-making Resistance of Ships. 287 
10 {S 20 VKnors 25 30 3s 40 45 50 
error are not known. The interrupted curve is a curve R = AV‘ sketched in 
for comparison. 
Table IV. 
v R. V. 
10 1°5 30 
14 4-2 34. 
18 15 38 
22 44 42 
26 62 46 
§5. Comparison with Experimental Results. 
Before examining further model curves we must express the previous 
formula in a form more suitable for calculation; we use the system of units 
in which model results are now generally expressed. R is given in lbs. 
per ton displacement of the ship, while instead of the speed V we use the 
ratio V/\/L, V being in knots and L in feet; this is called the speed-length 
ratio, and we shall denote it by c. The advantage of these units is that they 
utilise Froude’s law of comparison; from the experimental curve between 
R and ¢ we can write down at once the residuary resistance for a ship of any 
length and displacement at the corresponding velocity, provided the ship has 
the same lines and form as the model. Thus the constants which are left in 
the relation between R and ¢ depend only upon the lines of the model, not 
upon its absolute size. At present we make no attempt to connect these 
constants with the form of the model, as expressed by the usual coefficients 
45 
